Digital subscriber line (DSL) technology provides high-speed data transfer between two or more modems or multicarrier apparatuses across ordinary telephone lines (e.g., twisted pair of copper wires), while still providing for plain old telephone service (POTS). Asynchronous Digital Subscriber Line (ADSL) and Very High Digital Subscriber Line (VDSL) have emerged as popular implementations of DSL systems, where ADSL is defined by American National Standard Institute (ANSI) standard T1.413 and International Telecommunication Union (ITU-T) standards G.992.3, G.992.5, and VDSL is defined by ANSI standard T1.424 and ITU-T standard G.993.1. ADSL, VDSL and other similar DSL systems (collectively referred to as “xDSL”) typically provide digital data transfer in a frequency range above the POTS band (e.g., about 300 Hz to 4 kHz), for example ADSL G.992.3 operates at frequencies from about 25 kHz to about 1.1 MHz. Packet-based technology (e.g., ITU G.hn, HomePNA, HomePlug® AV and Multimedia over Coax Alliance (MoCA)) also provides high-speed data transfer for multicarrier apparatuses. Some multicarrier apparatuses may be enabled to communicate using IEEE 802.11 and IEEE 802.16 (WiMAX) wireless technologies.
One feature of such multicarrier apparatuses that allows them to provide high data rates is their ability to communicate symbols over a multi-carrier channel. Such a multi-carrier channel may include a number of frequencies or “carriers” (e.g., carriers f1, f2, . . . fN) that span a frequency spectrum supported by the telephone line or other communication medium. In effect, by breaking the frequency spectrum into multiple carriers, the multicarrier apparatuses can transmit data over each of the carriers (instead of just a single carrier), thereby allowing them to “stuff” more data through the communication medium (e.g., telephone twisted pair).
During communication, a specific number of bytes per unit time may be transmitted on each carrier based on a signal-to-noise ratio (SNR). Typically, more bytes are transmitted on carriers that have a relatively high SNR, while fewer bytes are transmitted on frequencies that have a relatively low SNR. Although encoding and decoding data conveyed on multiple frequencies makes multicarrier communication computationally complex, it gives the multicarrier apparatuses the ability to provide users with high speed data connections with relatively few errors.
Although a multicarrier channel affords communication systems some ability to account for particularly noisy regions of the frequency spectrum, other components are typically used to account for more dynamic noise sources, such as impulse noise. Therefore, to achieve high data rates with high accuracy, improvements can be made to allow communication systems to communicate more efficiently.